Alternatively, in the words of the Ecclesiarch Decius:
-A paraplegic sociopath
-Never went to rehab
-Supernatural garbage bag
-An indecisive mollusk
-Doesn't exist, shut up about it
-Man-Emperor of Mankind
-A fucking clown
-Big Daddy Calgar's personal pleasure object
-Supernatural garbage can
-Literal mushroom
-Literal mushroom
-Straight up an idiot
-Has no friends
-Decius hasn't spoken about the Void Dragon and Outsider, but the Emperor did make fun of them for being "edgy" and having names "only the loneliest of people could come up with" (though I may be paraphrasing)

Also, Slaneesh is surprisingly cute-looking here in spite of being, well, Slaneesh.

You forgot the Ultrasmurfs: